As many as 60% of breast cancer (BrCA) patients receiving radiation are known to develop fatigue with about 30% suffering persistent fatigue several months to years after treatment completion (12-23). The physical, psychological, and molecular mechanisms by which patients develop fatigue are poorly understood and most likely multi-factorial. One pathway that has received considerable attention is nuclear factor-kappa B (NF-kB)(24). The NF-kB pathway has emerged as having an important role not only in cancer treatment resistance but in the development of fatigue. NF-kB activation leads to over expression of interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha, all factors related to inflammation and factors that have been found to be upregulated in patients receiving radiation as well as BrCA survivors with fatigue (25-29). A recently published study looking at TNF-alpha, fatigue and cachexia in cancer patients receiving docetaxol showed that NF-kB is upregulated in fatigued patients and that agents which inhibit TNF-alpha lead to better tolerance of chemotherapy dose escalation (30). Work by our group and others has shown that ionizing radiation increases NF-kB pathway activity in circulating immune cells (as well as within breast cancer cells) and that this effect is most pronounced in women previously treated with chemotherapy (31, 32). Our work has shown that the NF-kB pathway activity in circulating immune cells is also related to fatigue development in BrCA patients treated with radiation and that patients most at risk for persistent fatigue and NF-kB pathway activity are those who have received chemotherapy for their breast cancer (31).